Doherty power amplifier architectures are increasingly used as replacement for more traditional Class B amplifier in base-station and broadcast applications. Doherty amplifiers are simple in construction and highly efficient in performance. However, despite of its success, practicable implementations of Doherty power amplifier architectures may be rather limited in RF bandwidth, a problem that tends to be exacerbated towards higher power levels.
With Doherty power amplifier architectures being widespread due to their increased efficiency performance, linearity and operating bandwidth are typically deteriorated. Class C biased peaking amplifiers may causes AM-PM distortion, thereby limiting the overall amplifier linearity. Additionally, combiner devices for the output power are often regarded as the constraining factor for achievable RF bandwidth. Doherty power amplifier architectures are typically used in narrowband scenarios and commonly accompanied by pre-distortion input circuitry.
Specifically in frontend applications Doherty power amplifier architectures have become the quasi-linear architecture of choice. As microwave or millimeter wave air interface become more common, particularly with the advent of 5G communication technologies, the conventionally used amplifier classes as constituents of the Doherty architecture impose severe restrictions to its applicability which have hitherto been tried to address with different approaches.
Document WO 2007/117189 A1 discloses a method and a system for compensating signal distortions in multiple transmitting branches of a composite amplifier. Document WO 2007/078217 A1 discloses a detuned composite amplifier with a nonlinear drive function having a phase that varies with the composite amplifier output voltage amplitude and being configured to transform the output voltage transition point into an extended output voltage transition region to increase the efficiency of the composite amplifier. Document US 2014/0085000 A1 discloses a Doherty-type amplifier with a main-amplifier circuit, an auxiliary-amplifier circuit and a signal-generating device. Document US 2015/0116039 A1 discloses a multi-path amplifier system with an adjustable power splitter. Document U.S. Pat. No. 8,354,882 B2 discloses a Doherty amplifier with an optimized input network for MMIC integration.